NiFe Layer Research Articles

Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves

Brillouin light scattering (BLS) was exploited to study the spin wave properties of spin-valve (SV) type samples basically consisting of two 5 nm-thick NiFe layers (separated by a Cu spacer of 5 nm), differently biased through the interface exchange coupling with an antiferromagnetic IrMn layer. Three samples were investigated: a reference SV sample, without IrMn (reference); one sample with an IrMn underlayer (10 nm thick) coupled to the bottom NiFe film; one sample with IrMn underlayer and overlayer of different thickness (10 nm and 6 nm), coupled to the bottom and top NiFe film, respectively. The exchange coupling with the IrMn, causing the insurgence of the exchange bias effect, allowed the relative orientation of the NiFe magnetization vectors to be controlled by an external magnetic field, as assessed through hysteresis loop measurements by magneto-optic magnetometry. Thus, BLS spectra were acquired by sweeping the magnetic field so as to encompass both the parallel and antiparallel alignment of the NiFe layers. The BLS results, well reproduced by the presented theoretical model, clearly revealed the combined effects on the spin dynamic properties of the dipolar interaction between the two NiFe films and of the interface IrMn/NiFe exchange coupling.

Effects of annealing temperature on the magnetoresistance in Ta/NiFe/Ta films by ZnO intercalations

Zinc oxide (ZnO) exhibiting many superior physical properties was inserted into the Ta/NiFe/Ta films as nano-oxide intercalations. Different annealing temperatures and ZnO thickness significantly affected the magnetoresistance (MR) in NiFe films. The 4-nm thick ZnO film annealed at 200°C had a MR of 2.41%, which was more than 70% higher than that of the 1-nm thick ZnO annealed film (MR=1.40%). However, the further increase in annealing temperature to 300°C rapidly deteriorated the MR performance of the films. Diffusion and interface reactions occur between the crystal ZnO and the adjacent NiFe layer. Lower-temperature annealing improved the interface, increasing the specular reflection of spin-polarized electrons to some extent. However, higher-temperature annealing induced severe diffusion and interface reactions, which led to a sharp decline in MR performance.

Low-frequency alternative-current magnetic susceptibility, photoelectric properties, and adhesive properties of Ni80Fe20 (XÅ)/ZnO(500Å) and ZnO(500Å)/Ni80Fe20(YÅ) on glass substrate

The following conditions are deposited: (a) glass/Ni80Fe20(XÅ)/ZnO(500Å) and (b) glass/ZnO(500Å)/Ni80Fe20(YÅ), where each of X and Y is 1000Å, 1500Å, 2000Å or 2500Å. The substrate temperature was maintained at room temperature (RT), and post-annealing was performed with heating at (TA)=150°C for 1h or (TA)=250°C for 1h. The sputtering sequence and the thickness of the NiFe film were varied to study the effects of these factors on the low-frequency alternative-current magnetic susceptibility (χac), maximum χac with corresponding optimal resonance frequency (fres), transmission, electrical resistivity (ρ), and surface energy of the multilayered glass/Ni80Fe20(XÅ)/ZnO(500Å) and glass/ZnO(500Å)/Ni80Fe20(YÅ). Experimental results demonstrate that ZnO(500Å)/Ni80Fe20(YÅ) is superior to Ni80Fe20/ZnO(500Å) because diffraction from the ZnO (002) crystals at the bottom of ZnO(500Å)/Ni80Fe20(YÅ) improves the magneto crystalline anisotropy of Ni80Fe20, improving its magnetic and photoelectrical properties. X-ray diffraction patterns (XRD) reveal that the ZnO (002), ZnO (220), and NiFe (111) peaks of ZnO(500Å)/Ni80Fe20(YÅ) are more intense than those of Ni80Fe20/ZnO(500Å) under three substrate conditions, indicating the ZnO (002) peak reflects magneto crystalline anisotropy in the crystalline NiFe layer of ZnO(500Å)/Ni80Fe20(YÅ), yielding the highest χac of approximately 3.16 with an fres of 250Hz upon post-annealing TA=250°C for 1h. The (111) diffracted intensity and grain size of the thicker and post-annealed Ni80Fe20 thin films exceeded those of the thinner and as-deposited Ni80Fe20 thin films. A spectral analyzer was used to measure transmittance through NiFe of various thicknesses. The transmittance declined slightly as the thickness and grain size increased, because increasing thickness reduced penetration. Post-annealing promoted grain growth, increased the average size of the grains and reduced transmittance. Both as-deposited glass/Ni80Fe20(XÅ)/ZnO(500Å) and as-deposited glass/ZnO(500Å)/Ni80Fe20(YÅ) had the highest penetration, when X, Y=1000Å, and the highest transmittances of 87% and 93%, respectively. The highest transmittance of glass/ZnO(500Å)/Ni80Fe20(YÅ) exceeded that of glass/Ni80Fe20(XÅ)/ZnO(500Å) owing to ZnO (002) crystallization. Furthermore, ρ decreased as the Ni80Fe20 thickness increased, because grain boundaries and the surface of thin films scattered the electrons, so thinner films had greater resistance. Electrical measurements revealed that the maximum resistivities of glass/Ni80Fe20(1000Å)/ZnO(500Å) and glass/ZnO(500Å)/Ni80Fe20(1000Å) were 292μΩcm and 288μΩcm, and the resistivity declined as the thickness of the film increased. The surface energy of the as-deposited and thinner NiFe layers exceeded that of post-annealed and thicker NiFe layers, revealing that the adhesion of the as-deposited and thinner NiFe films was stronger than that of the post-annealed and thicker films, on account of the degrees of crystallinity. Glass/Ni80Fe20(1000Å)/ZnO(500Å) and glass/ZnO(500Å)/Ni80Fe20(1000Å) had the highest surface energies of 64mJ/mm2 and 59mJ/mm2; the surface energy worsened as the temperature increased, suggesting that the adhesion of the as-deposited and thinner NiFe films in glass/Ni80Fe20(XÅ)/ZnO(500Å) was stronger than in glass/ZnO(500Å)/Ni80Fe20(YÅ). The results indicate that the magnetic and photoelectric properties of glass/ZnO(500Å)/Ni80Fe20(YÅ) were better than those of glass/Ni80Fe20(XÅ)/ZnO(500Å) because the strong ZnO (002) crystallization in ZnO(500Å)/Ni80Fe20(YÅ) increased the magneto crystalline anisotropy NiFe (111) and importantly affected the magnetic and photoelectrical properties.

Spin pumping and inverse Rashba-Edelstein effect in NiFe/Ag/Bi and NiFe/Ag/Sb

The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling in surface or interface states. We measured the inverse Rashba-Edelstein effect via spin pumping in Ag/Bi and Ag/Sb interfaces. The spin current is injected from the ferromagnetic resonance of a NiFe layer towards the Rashba interfaces, where it is further converted into a charge current. Using spin pumping theory, we quantify the conversion parameter of spin to charge current to be 0.11 ± 0.02 nm for Ag/Bi and a factor of ten smaller for Ag/Sb. The relative strength of the effect is in agreement with spectroscopic measurements and first principles calculations. We also vary the interlayer materials to study the voltage output in relation to the change of the effective spin mixing conductance. The spin pumping experiment offers a straight-forward approach of using spin current as an efficient probe for detecting interface Rashba splitting.

Tantalum Nitride Nanorod Arrays: Introducing Ni–Fe Layered Double Hydroxides as a Cocatalyst Strongly Stabilizing Photoanodes in Water Splitting

Ta3N5 nanostructures are widely explored as anodes for photoelectrochemical (PEC) water splitting. Although the material shows excellent semiconductive properties for this purpose, the key challenge is its severe photocorrosion when used in typical aqueous environments. In the present work we introduce a NiFe layered double hydroxide (LDH) cocatalyst that dramatically reduces photocorrosion effects. To fabricate the Ta3N5 electrode, we use through-template anodization of Ta and obtain oxide nanorod arrays that then are converted to Ta3N5 by high temperature nitridation. After modification with our cocatalyst system, we obtained solar photocurrents of 6.3 mA cm–2 at 1.23 VRHE in 1 M KOH, and an electrode maintains about 80% of the initial activity for extended irradiation times.

Interfacial exchange coupling induced anomalous anisotropic magnetoresistance in epitaxial γ'-Fe₄N/CoN bilayers.

Anisotropic magnetoresistance (AMR) of the facing-target reactively sputtered epitaxial γ'-Fe4N/CoN bilayers is investigated. The phase shift and rectangular-like AMR appears at low temperatures, which can be ascribed to the interfacial exchange coupling. The phase shift comes from the exchange bias (EB) that makes the magnetization lag behind a small field. When the γ'-Fe4N thickness increases, the rectangular-like AMR appears. The rectangular-like AMR should be from the combined contributions including the EB-induced unidirectional anisotropy, intrinsic AMR of γ'-Fe4N layer and interfacial spin scattering.

Resonant spin-wave modes in trilayered magnetic nanowires studied in the parallel and antiparallel ground state

Brillouin light scattering has been utilized to study the field dependence of resonant spin-wave modes in layered NiFe(30nm)/Cu(10nm)/NiFe(15nm)/Cu(10nm)/NiFe(30nm) nanowires of rectangular cross section, 150nm wide and formed in arrays that are spaced laterally by 400nm. The major and minor longitudinal hysteresis curves have been measured by the magneto-optical Kerr effect technique, with applied field parallel to the length of the nanowires. The light-scattering spectra were recorded as a function of the magnetic field strength, encompassing both the parallel and antiparallel alignments of the middle stripe with respect to the magnetization direction of the outermost ones. The field ranges for the antiparallel state are different from those for the parallel case, while the mode frequencies change abruptly at the parallel-to-antiparallel transition field (and vice versa). The modes detected in the antiparallel state are found to have only a weak dependence on the applied magnetic field, whether along the major or minor hysteresis curves, while in the parallel state the mode frequencies monotonically increase with the applied magnetic field. The experimental results have been successfully interpreted, across the whole range of the magnetic fields investigated, in terms of the mode localizations across the width and in the layered structure. This was accomplished by means of a microscopic (Hamiltonian-based) theory, which has been extended here to the case of non-parallel magnetic ground states.

Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 Å, the thickness of the Cu spacer was varied from 5 to 50 Å. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm2 for the sample with a 5 Å Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

XPS analyses on Ta/Au/NiFe/NiO/Ta films

In this study, Ta/NiFe/NiO/Ta films were prepared by magnetron sputtering. The Au layer inserted at the interface of Ta and NiFe significantly influences the exchange bias field (Hex) of the Ta/NiFe/NiO/Ta films. The Hex of the film with 0.9 nm Au layer increased by 28% compared with that of the film without a Au layer. The results show that the Au layer inserted at the interface of Ta and NiFe segregated at the surface of the NiFe/NiO in Ta/Au/NiFe/NiO/Ta films. The Au layer insulated the direct contact and suppressed the interface reaction between the NiFe and NiO layers, thus increasing the Hex. Copyright © 2015 John Wiley & Sons, Ltd.

Deposition temperature mediated tunable tilt angle magnetization in Co–Pt/Ni81Fe19 exchange springs

Abstract In this study, we investigate the effect of deposition temperature of Co–Pt fixed layer, T d,CoPt (150, 250 and 350 °C) on the tilt angle magnetization ( θ M ) of Ni 81 Fe 19 -layer grown at room temperature (RT) and at different thicknesses ( t NiFe =0, 1.0, 2.5 and 4.0 nm) in Co–Pt( T d,CoPt )/NiFe( t NiFe ) exchange springs. The magnetic studies demonstrated a strong perpendicular magnetic anisotropy (PMA) for the equi-compositional ordered Co–Pt layer grown on glass substrate using the film sequence: Ta(20 nm)/Pt(20 nm)/CoPt(5 nm), regardless of T d,CoPt . The PMA can be retained with the addition of a 4-nm NiFe layer on the top when T d,CoPt ≥250 °C. In contrast, relatively a thin layer of Ni–Fe (2.5 nm) can destroy the perpendicular exchange-spring behavior if the Co–Pt layer is deposited at RT. Using 3-D micromagnetic simulation, the interfacial exchange coupling strength ( A ij ) between the Co–Pt and NiFe-layers was estimated and the A ij value is found to increase rapidly when T d,CoPt is increased from RT to 300 °C. Besides, the magnetization tilted angle ( θ M ) of NiFe can be easily tuned from completely out-of-plane to almost 60° when t NiFe =4.0 nm. Through this study, it is demonstrated that the θ M of NiFe-layer can be tuned by not only altering the t NiFe ; but also by varying the T d,CoPt .

Enhanced planar hall sensitivity with better thermal stability by introducing interfacial modification of Au spacer

Abstract This paper reports an enhancement of planar Hall sensitivity in NiFe/Au/IrMn multilayers by introducing interfacial modification. The improvement of the sensitivity derives from the increase of resistivity change (Δρ), which is attributed to strengthened spin-asymmetry of polarized electrons in NiFe layer induced by strong spin–orbit scattering of Au layer. Furthermore, the NiFe/Au/IrMn structure based sensor exhibits good thermal stability. The high sensitivity together with good thermal stability makes the NiFe/Au/IrMn structure based sensor very promising for bio-detections.

Magnetic structure and anisotropy of[Co/Pd]5/NiFemultilayers

The magnetization behavior, magnetic anisotropy, and domain configurations of Co/Pd multilayers with perpendicular magnetic anisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy, and ferromagnetic resonance. The thickness of the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ layer in ${[\mathrm{Co}/\mathrm{Pd}]}_{5}/\mathrm{NiFe} (t)$ was varied from $t=0$ to 80 nm in order to study the interplay between the anisotropy and magnetization directions of Co/Pd and NiFe. By varying the thickness of the NiFe layer, the net anisotropy changes sign, but domains with plane-normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed-anisotropy thin films can be controlled.

Perpendicularly magnetized L1-FePt nanodots exchange-coupled with soft magnetic Ni81Fe19

We studied exchange-coupled bilayers consisting of a perpendicularly magnetized L10-FePt layer and a soft magnetic Ni81Fe19 (Permalloy; Py) layer, where the Py layer was thick enough to form spatially twisted magnetic structures. The Py layer showed in-plane magnetization in the case of unpatterned thin film because of its demagnetizing field even though Py was exchange-coupled to the perpendicularly magnetized L10-FePt layer at the interface. After patterning the FePt/Py bilayer into nanosized dots with cylindrical shape, the effective perpendicular magnetic anisotropy was induced. Exchange-coupling behavior, i.e., spring back behavior, was observed when the minor magnetization curves were measured. In addition to this behavior, the magnetic domain observation suggested that a spatially twisted magnetic structure was formed with sweeping the perpendicular magnetic field.

Synthesis of Nitrogen-Doped Carbon Nanocoils with Adjustable Morphology Using Ni—Fe Layered Double Hydroxides as Catalyst Precursors

Nitrogen-doped carbon nanocoils (CNCs) with adjusted morphologies were synthesized in a one-step catalytic chemical vapour deposition (CVD) process using acetonitrile as the carbon and nitrogen source. The nickel iron oxide/nickel oxide nanocomposites, which were derived from nickel–iron layered double hydroxide (LDH) precursors, were employed as catalysts for the synthesis of CNCs. In this method, precursor-to-catalyst transformation, catalyst activation, formation of CNCs, and nitrogen doping were all performed in situ in a single process. The morphology (coil diameter, coil pitch, and fibre diameter) and nitrogen content of the synthesized CNCs was individually adjusted by modulation of the catalyst composition and CVD reaction temperature, respectively. The adjustable ranges of the coil diameter, coil pitch, fibre diameter, and nitrogen content were confirmed to be approximately 500±100 nm, 600±100 nm, 100±20 nm, and 1.1±0.3 atom%, respectively.

Application Prospects of Multilayer Film Shields for Space Research Instrumentation

We have studied the magnetic properties of multilayer film cylindrical configuration shields (MFS) based on NiFe / Cu. The studied samples were prepared by electrode position. MFS were constituted by alternating layers of NiFe and Cu, deposited on an aluminum cylinder with diameter of 4cm, length of 13cm and 0.5cm thickness. The thickness of each ferromagnetic layer varied from 10 to 150μm, and the thickness of Cu layers was 5μm. Five-samples in which the number of ferromagnetic layers varied from 3 to 45 and copper – from 2 to 44 were tested. The best shielding efficiency was achieved at the maximum number of layers and comprised about 102. Permalloy multilayer foil shield at the same total thickness has several times less efficiency in comparison with MFS. The description of a prototype of the charged particles telescope for space application is presented. Results of its testing regarding sensitivity to the constant magnetic field are described.

Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance

Exchange-coupled hard and soft magnetic layers find extensive use in data storage applications, for which their dynamical response has great importance. With bulk techniques, such as ferromagnetic resonance (FMR), it is difficult to access the behaviour and precise influence of each individual layer. By contrast, the synchrotron radiation-based technique of x-ray detected ferromagnetic resonance (XFMR) allows element-specific and phase-resolved FMR measurements in the frequency range 0.5–11 GHz. Here, we report the study of the magnetization dynamics of an exchange-coupled Ni0.81Fe0.19 (43.5 nm)/Co0.5Fe0.5 (30 nm) bilayer system using magnetometry and vector network analyser FMR, combined with XFMR at the Ni and Co L2 x-ray absorption edges. The epitaxially grown bilayer exhibits two principal resonances denoted as the acoustic and optical modes. FMR experiments show that the Kittel curves of the two layers cannot be taken in isolation, but that their modelling needs to account for an interlayer exchange coupling. The angular dependence of FMR indicates a collective effect for the modes of the magnetically hard CoFe and soft NiFe layer. The XFMR precessional scans show that the acoustic mode is dominated by the Ni signal with the Co and Ni magnetization precessing in phase, whereas the optical mode is dominated by the Co signal with the Co and Ni magnetization precessing in anti-phase. The response of the Co signal at the Ni resonance, and vice versa, show induced changes in both amplitude and phase, which can be ascribed to the interface exchange coupling. An interesting aspect of phase-resolved XFMR is the ability to distinguish between static and dynamic exchange coupling. The element-specific precessional scans of the NiFe/CoFe bilayer clearly have the signature of static exchange coupling, in which the effective field in one layer is aligned along the magnetization direction of the other layer.

Effects of interfacial roughness on the planar Hall effect in NiFe/Cu/IrMn multilayers

This paper reports that the planar Hall effect in NiFe/Cu/IrMn multilayers was strongly influenced by the Cu spacer thickness (t Cu), which was due to the variation of interfacial roughness. With t Cu increasing, a peculiar change of planar Hall voltage was observed. The reason for the voltage behaviors was that the interfacial roughness influenced the spin-asymmetry of spin-polarized electrons in ferromagnetic metals. The diffuse scattering to the electrons turned to specular scattering when the interface became flat, leading to the variation of resistivity change (Δρ). As the increase in t Cu, the extremum field was reduced because of the weaken exchange coupling between NiFe and IrMn layers.

Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors

In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

FeNi-based flat magnetoimpedance nanostructures with open magnetic flux: New topological approaches

Classic flat MI multilayers consist of top and bottom ferromagnetic parts of equal thickness separated by a conductive lead. In previous studies symmetric MI structures were considered because they provide the highest sensitivity with respect to uniform external magnetic fields. There are a number of applications where non-uniform magnetic fields of complex configurations must be detected. Non-symmetric MI structures can be advantageous in this particular case. We describe our experience in design, fabrication and characterization of symmetric and non-symmetric MI multilayers with open magnetic flux. Non-symmetry of the structures was obtained by the deposition of top and bottom ferromagnetic parts of MI element of different thickness. MI responses of the structures with even or odd configurations of the FeNi layers were also considered.

Microstructural and magnetic characterization of ion-beam bombarded [Ni80Fe20-Cr]50 thin films

Ion-beam bombardment during thin film deposition can effectively change the microstructure and thus influence the magnetic properties of the thin film system. In this paper, we studied plain (un-bombarded) and argon ion-beam bombarded multilayered [Ni80Fe20-Cr]50 thin films fabricated using a dual ion-beam deposition technique. The atomic force microscopy images of the bombarded thin films showed a much rougher surface and an increased average grain size. No noticeable exchange bias phenomenon was observed in the thin films deposited with or without bombardment, indicating that the interfacial uncompensated spins were prevented from providing the necessary unidirectional anisotropy due to interfacial intermixing. This significant intermixing between Ni80Fe20 and Cr layers, and the etching process caused by the bombardment, led to the formation of an nano-composite [Ni80Fe20-Cr]50 thin film with a reduced Curie temperature. An enhancement of the coercivity attributed to the stronger NiFe–Cr coupling was also found, which was the result of additional pinning sites created by the bombardment. The bombarded thin film also exhibited a higher ZFC/FC divergence temperature compared to the un-bombarded film, which indicated a much stronger NiFe–Cr coupling and more coordinated alignment of the magnetization of the film's larger crystallites.